The primary driver for expansion in modern college football is tv viewers. Conference want access to market and subsequent tv deals. If BYU was in a more populated area that is also closer to other populated areas, I have no doubt they would be in P5 conference long ago.

The fact is BYU is far away and provides access to only a single and very middle ground tv market. At this point expansion is all driven by money. The Big12 doesn't have to expand, they aren't grasping at straws to save the conference (your welcome TCU and WVU). Addition has to make obvious fiscal sense and right now adding anybody (including BYU) does't make obvious fiscal sense.

Now if push comes to shove BYU is at or near the top of the list.